The present invention relates to an image display apparatus which comprises a flat face plate having a phosphor screen on the inner surface thereof, a flat rear plate opposed to the face plate, plate support portions arranged between the face plate and the rear plate to support an atmospheric pressure load, and an electron emission portion provided on the rear plate, and relates to as well as a method of manufacturing the image display apparatus.
In recent years, various discussions and studies have been made in relation to high-definition broadcasting or an image display apparatus of a high resolution having a large screen which responds to such broadcasting. For example, in a cathode ray tube serving as the image display apparatus, in order to achieve a high resolution, the beam spot diameter of each electron beam on the phosphor screen must generally be reduced.
In this respect, improvements in the electrode structure of an electron gun or enlargement and extension of the diameter of an electron gun itself have been attempted, but have not reached satisfactory results. This is because the distance from an electron gun to a phosphor screen increases as the size of a cathode ray tube is enlarged, so that the magnification of the electron lens is enlarged too much. Therefore, the distance (or depth) from an electron gun to a phosphor screen must be reduced to achieve a high resolution. In addition, a widened deflection angle of an electron beam leads to an increase of a difference in magnification between the center of a screen and the periphery thereof. Deflection at a widened angle is thus not a better way to achieve a high resolution.
Hence, developments have been made to a cathode ray tube as a solution for the problem of a conventional cathode ray tube as described above, for example, Japanese Patent Application KOKAI Publication No. 5-36363 discloses a cathode ray tube wherein a face plate and a rear plate are flattened, and a plurality of regions of a phosphor screen with an integrated structure formed on the inner surface of the face plate are dividedly scanned by electron beams emitted from a plurality of electron guns which are attached to the rear plate.
More specifically, this kind of cathode ray tube comprises a flat face plate and a rear plate made of glass and opposed in parallel to each other, and a side wall made of glass is joined to the periphery of the face plate so as to extend vertically, for example, using a joining material such as frit glass or the like. The rear plate is fixed to the face plate through the side wall. A plurality of rectangular openings are formed in the rear plate, corresponding to a plurality of regions to be scanned dividedly. Also, a plurality of funnels are fixed by a joining material, to the rear plate so as to surround the respective openings, and the electron guns are respectively arranged in the necks of the funnels. Further, a plurality of plate support members are disposed between the face plate and the rear plate and support the face and rear plates against an atmospheric pressure load. Each plate support member is formed of metal in a columnar shape and has a base end joined to the inner surface of the rear plate by frit glass or the like and a top end in contact with the inner surface of the face plate.
Further, a plurality of regions of the phosphor screen with an integrated structure formed on the inner surface of the face plate are dividedly scanned by electron beams emitted from the plurality of electron guns. Images respectively displayed on the regions by the divisional scanning are connected together by controlling signals applied to the electron guns or deflectors equipped so as to correspond to the electron guns, so that a seamless image is reproduced over the entire regions of the phosphor screen, without an overlap.
In the image display apparatus comprising a plurality of plate support members as described above, the plate support members must be correctly arranged at predetermined positions and the heights of the top end portions thereof must be aligned uniformly in order to efficiently support the face plate and the rear plate by the plate support members.
However, in a conventional image display apparatus, it is difficult to align heights of all the plurality of plate support members and it is also very difficult to join the plate support members precisely without displacements because each plate support member is joined to the rear plate by a joining material.
Further, in a cathode ray tube wherein a plurality of regions of the phosphor screen are dividedly scanned by electron beams emitted from a plurality of electron guns, as described above, the electron guns must be correctly situated at predetermined positions such that the axes of the electron guns pass through the respective centers of the corresponding regions, in order to set the raster of each region to a predetermined size and thereby to obtain an image without seams and overlaps between adjacent regions.
However, in the conventional cathode ray tube, it is very difficult to join a plurality of funnels to the rear plate with high precision such that the axes of the electron guns enclosed in the necks of the funnels pass through the respective centers of the regions. Further, the plurality of funnels and the side wall must be fixed to the rear plate made of glass by a joining material. The joining portions thereof decrease positional precision of its respective components, as well as reliability concerning the ability to withstand-voltage and maintain vacuum-air-tightness.